The present invention relates to a motor-generator system for a motor vehicle with hybrid traction drive.
German Laid-Open Publication DE 44 44 545 A1, for instance, discloses the basic construction principles of hybrid traction drives, on which the present invention is based. In traction operation, an internal combustion engine and/or an electric machine that is supplied with current by a battery, drive the vehicle either alone or jointly. On the other hand, in braking operation or the like, the electric machine, as a generator, recovers energy and supplies it to the battery. In the aforementioned prior art, in order to increase the range achievable by the traction drive of the electric machine, an additional generator driven by the internal combustion engine is provided for charging the battery. Japanese Laid-Open Publication JP 07 23 1502 A discloses an induction motor in which the battery is charged without the need for an independent charger.
One object of the present invention is to better utilize the investment that is required for the basic structure of a motor-generator system. A related object is to expand the range of application of a vehicle equipped with such a motor-generator system.
According to the invention, these and other objects are attained by a motor-generator system for a motor vehicle with hybrid traction drive that includes an internal combustion engine, an electric machine operable as a drive motor or as a generator driven by the internal combustion engine, a first stator winding assigned to the traction drive, a second stator winding assigned to stationary isolated generator operation of the electric machine, and external power consumers that are electrically supplied via the second stator winding.
The inventive motor-generator system jointly uses the basic equipment that is already installed for the traction drive and merely adds essentially one additional stator winding. This permits a vehicle equipped with the inventive motor-generator system to be used for stationary isolated generator operation as a so-called utility vehicle, to supply stationary power consumers, e.g. tools such as drills, electric saws or pumps, on construction sites or similar xe2x80x9cislandsxe2x80x9d where domestic power grid connections are not or are not yet available.
The additional stator winding provided in the electric machine may be separated from the existing first stator winding. Preferably, the additional stator winding is electrically insulated from the first stator winding but is accommodated in the same laminated core, preferably in common slots. Advantageously, the additional stator winding is used in traction operation as an additional electric booster, and in generator operation for increased recharging of the battery. The electric machine is preferably embodied as an asynchronous machine with a squirrel cage rotor, in particular in view of the middle-level power requirements for these types of uses.
Advantageously, the already existing converter device can be jointly used, for voltage control and VAr (reactive power) control of the second stator winding. For this purpose, the second stator winding is transformer-coupled to the first stator winding, and to those devices controlling the first stator winding, in the same laminated core that receives the first stator winding. Although the converter device supplies a pulse-width modulated voltage that is only approximately sinusoidal, the transformer coupling of the second stator winding to the first stator winding has the advantage of achieving a filter effect, such that the harmonic content of the output voltage is reduced and its shape thereby better approximates the desired sinusoidal curve.